Capacitive number wheel encoder for utility meters

ABSTRACT

A number wheel assembly (10) for a counter mechanism has a plurality of number wheels (13-18), each number wheel (13-18) having a sleeve (48) around its circumference with a plurality of positions representing successive increments in a count, a substrate (26-31) opposite one surface of the number wheel (13-18), the substrate (26-31) carrying an electrode (42) that is spaced from the number wheel (13-18) to form an air gap for a variable capacitor, and wherein the number wheel (13-18) carries at least one dielectric element (46) that is rotated with the number wheel (13-18) to vary the capacitance of the variable capacitor according to the position of the number wheel (13-18). Circuitry for detecting the capacitance and the position of the number wheels (13-18) is provided on a circuit board (39) that is electrically connected to the number wheels (13-18).

TECHNICAL FIELD

The invention relates to meter registers for counting units ofconsumption in utility meters.

BACKGROUND ART

Registers for utility meters have typically used some form of digitalcounting device for recording units of consumption.

Klyce, U.S. Pat. No. 3,543,259 and King et al., U.S. Pat. No. 4,924,407,show capacitive-type meter reading devices. These devices are designedfor use with dial-type meter registers.

Another type of meter register utilizes number wheels similar toodometers used in a wide variety of counting devices. This type ofcounting devices often use some type of contact system with contacts onthe number wheel which contact a reference contact for detectingposition. Such contact systems encounter the problems associated withcontact systems in general, namely wear, shorting of contacts due toaccumulated moisture and corrosion.

There is a need in the art of utility meters for non-contact encoderthat is not subject to contact oxidation and wear.

SUMMARY OF THE INVENTION

The invention relates to an improved rotatable element assembly for usein a non-contact encoder in the register of a utility meter.

The present invention is directed to new and improved capacitive-typeregister mechanisms to be applied, in the first instance, to utilitymeters.

The device comprises at least one rotatable element having acircumference with a plurality of positions representing successiveincrements in a count, a substrate opposite one surface of the rotatableelement, the substrate carrying an electrode that is spaced from therotatable element to form an air gap for a variable capacitor, andwherein the rotatable element carries at least one dielectric elementthat is rotated with the rotatable element to vary the capacitance ofthe variable capacitor.

The capacitance can be varied by varying the spacing of the air gapbetween the dielectric element and the electrode on the substrate. Thecapacitance can also be varied by varying a thickness of the dielectricelement opposite the electrode on the substrate.

The thickness of the dielectric element can be varied in a directionparallel to the axis of rotation of the rotatable element. The thicknessof the dielectric element can also be varied in a direction along aradius from the axis of rotation of the rotatable element.

In some embodiments, the rotatable element carries a second dielectricelement disposed adjacent said first-mentioned dielectric element andvarying inversely in thickness to said first-mentioned dielectricelement.

The thicknesses of the first and second dielectric elements can bevaried in a direction parallel to the axis of rotation of the rotatableelement. The thicknesses of the first and second dielectric elements canalso be varied in a direction along a radius from the axis of rotationof the rotatable element.

In another embodiment, the rotatable element carries a plurality ofdielectric elements in four tracks around its circumference to vary fourcapacitances and generate an analog-coded decimal pattern of capacitancesignals.

The non-contact nature of the invention allows the option of providingthin coatings of sealing material on the electrodes and dielectricelements to protect against moisture.

Other objects and advantages, besides those discussed above, will beapparent to those of ordinary skill in the art from the description ofthe preferred embodiment which follows. In the description, reference ismade to the accompanying drawings, which form a part hereof, and whichillustrate examples of the invention. Such examples, however, are notexhaustive of the various embodiments of the invention, and, therefore,reference is made to the claims which follow the description fordetermining the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view in elevation of a first embodiment of theinvention;

FIG. 2 is a sectional view taken in the plane indicated by line 2--2 inFIG. 1;

FIG. 3 is a sectional view taken in the plane indicated by line 3--3 inFIG. 1;

FIG. 4 is a sectional view taken in the plane indicated by line 4--4 inFIG. 3;

FIG. 5 is a side view in elevation of a second embodiment of theinvention;

FIG. 6 is a sectional view taken in the plane indicated by line 6--6 inFIG. 5;

FIG. 7 is a sectional view taken in the plane indicated by line 7--7 inFIG. 5;

FIG. 8 is a sectional view taken in the plane indicated by line 8--8 inFIG. 7;

FIG. 9 is a side view in elevation of a third embodiment of theinvention;

FIG. 10 is a sectional view taken in the plane indicated by line 10--10in FIG. 9;

FIG. 11 is a sectional view taken in the plane indicated by line 11--11in FIG. 9;

FIG. 12 is a sectional view taken in the plane indicated by line 12--12in FIG. 10;

FIG. 13 is a side view in elevation of a fourth embodiment of theinvention;

FIG. 14 is a sectional view taken in the plane indicated by line 14--14in FIG. 13;

FIG. 15 is a sectional view taken in the plane indicated by line 15--15in FIG. 13;

FIG. 16 is a sectional view taken in the plane indicated by line 16--16in FIG. 14;

FIG. 17 is a side view in elevation of a fifth embodiment of theinvention;

FIG. 18 is a sectional view taken in the plane indicated by line 18--18in FIG. 17; and

FIG. 19 is a sectional view taken in the plane indicated by line 19--19in FIG. 17; and

FIG. 20 is a schematic view of the ten rotational positions of thenumber wheels of FIG. 17; and

FIG. 21 is an electrical schematic view of a detection circuit whichconnects to the first through fifth embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-20 show a portion of meter register of the type used in utilitymeters to record consumption of units of gas, electricity and water. Notshown is a main portion of the meter in which a mechanical mover, suchas a water turbine, for example, is moved by the flow of fluid. Thismechanical mover is coupled to the present meter register through a geardrive which drives an assembly 10 of the present invention having sixnumber wheels 13, 14, 15, 16, 17 and 18.

To distinguish the parts in the various embodiments, the suffix "a"shall be used in numbering FIGS. 1-4, the suffix "b" shall be used inFIGS. 5-8, the suffix "c" shall be used in FIGS. 9-12, the suffix "d"shall be used in FIGS. 13-16 and suffix "e" shall be used in FIGS.16-20. Where the numbers appear in the description without a suffix,they shall refer to the corresponding parts with suffixes "a" through"e" in the five respective embodiments.

The meter register has a face with a window for viewing the portions ofthe number wheels 13-18 representing the count at any given time. In thefive preferred embodiments, the counter is a decade counter. Each numberwheel moves ten times to complete one full revolution and cause a nexthigher order number wheel to move 1/10 revolution. It should be apparentthat although the preferred embodiment is a decade counter, othercounters such as octal, could be constructed within the teaching of theinvention.

The number wheel assembly 10 has shaft 32a with ends 20a, 21a (FIG. 1)which extend from the ends of the number wheel assembly 10. A pluralityof pins 22a are formed on the lowest order number wheel 18a, for drivingthe wheel 18a. Teeth 23a are formed around one edge of wheels 13a-17a tobe driven by gears in the mechanical portion of the meter register unit.

FIGS. 1 and 5 show upright substrates that are supported by amotherboard PCB (printed circuit board) 39a, 39b. In FIGS. 9, 13 and 17,substrates are not necessary. FIG. 2 shows conductive electrodes 42a,43a on a side of substrate 36a facing the number wheel 16a. A positionelectrode 42a and a reference electrode 43a are connected by printedcircuit paths 44a, 45a to the motherboard 39a. These electrodes 42a, 43aform one plate of a variable capacitor and one plate of a referencecapacitor, respectively. The reference electrode 43a faces a portion ofthe hub 29a to form the reference capacitor having a fixed air gap.

Each number wheel 13a-18a has an thin annular element 46a of dielectricmaterial at a radial distance from an axis of rotation 47a passingbetween pins 20a, 21a. The annular surface 46a of each wheel extendsalong a spiral path around an axis of rotation 47a. This provides an airgap between electrodes 42a and dielectric surface 46a which varies as anumber wheel 13a-18a, such as number wheel 16a in FIG. 4, is rotated.

The electrodes 42a, 43a and the annular surface 46a are provided with acoating of a spray-on urethane material, such as Humi-Seal™ availablefrom Columbia Products, to protect against moisture accumulating onthese surfaces 42a, 43a, 46a.

The dielectric elements 46a of the number wheels 13a-18a are groundedthrough shaft end 21a.

Each number wheel has ten positions corresponding to areas oncircumference of wheel which carry digits from "0" to "9". The digitsare printed or applied as decals to Mylar sleeve 48a disposed on acircumference of each number wheel 13a-18a.

In operation, the variable capacitance is detected parallel to axis ofrotation 47a between active electrode 42a and grounded dielectricelement 46a. The reference capacitance is detected parallel to axis ofrotation 47a between reference electrode 43a and the hub 29a. Thevariable capacitance and fixed capacitance are then compared for eachwheel to determine the position of each number wheel, and thus a totalcount.

FIGS. 5-8 show an embodiment similar to FIGS. 1-4, with "b" numberedparts corresponding to similarly numbered "a" parts in FIGS. 1-4, exceptthat the dielectric element 46b is subdivided into two portions 49b and50b with different dielectric values per unit thickness.

The boundary 51b between first dielectric material 49b and seconddielectric material 50b spirals around axis 47b to vary thickness offirst dielectric material 49b and second dielectric material 50b atvarious positions around the number wheels 13b-18b.

The electrodes 42b, 43b and the annular surface 46a are provided with acoating of a spray-on urethane material, such as Humi-Seal™ availablefrom Columbia Products, to protect against moisture accumulating onthese surfaces 42b, 43b, 46b.

The number wheels 13b-18b each have ten positions corresponding to areason circumference of wheel which carry digits from "0" to "9". The digitsare printed or applied as decals to Mylar sleeve 48b disposed oncircumference of number wheel.

The variable capacitance is detected in a circuit which parallels theaxis of rotation 47b between active electrode 42b and dielectrics 49band 50b.

The reference capacitance is detected in a circuit which parallels theaxis of rotation 47b between reference electrode 43b and a referencehub, such as reference hub 29b, seen in FIG. 7.

The variable capacitance and fixed capacitance are then compared foreach wheel 13b-18b to determine the position of each number wheel, andthus a total count.

FIGS. 9-12 show an embodiment in which the reference capacitance and thevariable capacitance are formed in a radial direction relative to thenumber wheels 13c-18c. Again parts numbered with a "c" and a two-digitnumber found in FIGS. 1-8 correspond to similarly numbered "a" and "b"parts in FIGS. 1-8. Note, however, that there are no upright substrates26-31 in FIGS. 9-12, only motherboard PCB 39c. The shaft end 21c isgrounded as in the previous embodiments.

The position and reference electrodes 42c, 43c are now positioned on themotherboard PCB 39c facing circumferential surfaces of the number wheels13c-18c (FIG. 11). The printed circuit paths shown in the previousembodiments for electrodes 42, 43, are now internal to the motherboard39c.

Each number wheel 13c-18c has a circumferential element with a firstportion 29c of a thickness that varies in a radial direction from axisof rotation 47c (FIG. 10). The axial thickness of the first portion 29cis less than full width of wheel 13c-18c (FIGS. 9 and 12). Each numberwheel 13c-18c includes a second portion 51c positioned next to the firstportion 29c to form reference capacitor (FIG. 9).

Digits "0" to "9" are printed or applied as decals to a Mylar sleeve 48cdisposed on circumference of number wheel over conductive material 51cand dielectric material 46c.

A variable capacitance is detected in a radial direction between firstmotherboard electrode 42c and the first portion 46c (FIG. 10) ofdielectric material in a radial direction relative to axis of rotation47c (FIG. 9). A reference capacitance is detected between referenceelectrode 43c through conductive material 51c and ground plane in radialdirection relative to the axis of rotation 47c (FIG. 9).

The variable capacitance and fixed capacitance are then compared foreach wheel 13c-18c to determine the position of each number wheel, andthus a total count.

FIGS. 13-16 show an embodiment similar to FIGS. 9-12, except that asecond dielectric element 46d (FIG. 13) is disposed over the firstradial portion 29d and varies inversely in thickness to the firstdielectric element 29d in the radial direction from axis of rotation47d. The axial thickness of dielectric elements 46d and 51d is less thanfull width of each wheel 13d-18d (FIG. 12).

A variable capacitance is detected between first motherboard electrode42d through dielectrics 46d and 49d to in a radial direction relative toshaft 32d (FIG. 12).

A reference capacitance is detected between reference electrode 43dthrough material 51d in a radial direction relative to axis of rotation47d (FIG. 12).

The variable capacitance and fixed capacitance are then compared foreach wheel 13c-18c to determine the position of each number wheel, andthus a total count.

FIGS. 16-19 illustrate an number wheel assembly using variablecapacitance to generate analog-coded decimal signals. The number wheels13e-18e are carried by carrier assembly 40e having shaft 32e with shaftends 20e and 21e extending from opposite ends of the assembly along anaxis of rotation 47e for the number wheels 13e-18e. Each number wheel13e-18e has four circumferential tracks 52, 53, 54 and 55 (exemplifiedby track 52 in FIG. 17) each with four arcuate segments A, B, C and D ofrespective dielectric materials. Each track has segment A staggered withrespect to the position of segment A of the next track in the patternshown in FIGS. 17 and 20. The resulting Table 1 is the followingarrangement of the segments relative to ten rotational positions of eachnumber wheel 13e-18e.

                  TABLE 1                                                         ______________________________________                                        Position Track 52  Track 53  Track 54                                                                              Track 55                                 ______________________________________                                        1        A         D         D       D                                        2        A         A         D       D                                        3        B         A         A       D                                        4        B         B         A       A                                        5        C         B         B       A                                        6        C         C         B       B                                        7        C         C         C       B                                        8        D         C         C       C                                        9        D         D         C       C                                        0        D         D         D       C                                        ______________________________________                                    

On the motherboard 39e, aligned and facing tracks 52-55 are conductiveelectrodes 42e, 42f, 42g, 42h.

Digits "0" to "9" are printed or applied as decals to Mylar sleevedisposed on circumference of number wheels 13e-18e.

A set of four analog-coded variable capacitances are detected betweentracks 52, 53, 54 and 55 and respective electrodes 42e, 42f, 42g, 42h(FIG. 19). The pattern is then decoded in a manner known in the art byconventional circuitry on motherboard 39e.

FIG. 21 illustrates detection circuitry on motherboard for reading thecapacitances produced by the position of the number wheels 13-18 in thefour embodiments shown in FIGS. 1-16. The variable capacitances producedby the four embodiments in FIGS. 1-14 for number wheels 13-18 arerepresented by capacitors CA1, CA2, CA3, CA4, CA5 and CA6 in FIG. 21.The reference capacitances produced by the four embodiments in FIGS.1-14 for number wheels 13-18 are represented by capacitors CB1, CB2,CB3, CB4, CB5 and CB6 in FIG. 18. The ground connections in FIG. 18 areprovided by the ground planes in FIG. 4 and FIG. 8 for the first twoembodiments and are formed on the motherboard 39c, 39d for the third andfourth embodiments in FIGS. 9-14.

In FIG. 18, the switches S2-1 through S2-6 and switches S3-1 throughS3-6 are formed by a multiplexer 56 which is provided by a commercialcircuits such as the Maxim DG 406 multiplexer circuits. Switches S1, S4and S5 are provided by a commercial circuit such as the Maxim DG 442analog switching circuits.

A source of positive DC voltage is connected through switches S1 and S5to an noninverting (+) input of an operational amplifier OA1, which isprovided by an ICL 7614 circuit available from Maxim. The output of thisop amp OA1 is connected back to the inverting (-) input. A holdingcapacitor C3 is connected between the noninverting (+) input and ground.The output of the op amp OA1 is also connected to a noninverting (+)input of a comparator provided by a commercial circuit Max 922 availablefrom Maxim. The source of positive DC voltage (+V) is also connectedthrough voltage divider provided by resistors R1 and R2 to the inverting(-) input of the comparator circuit COMP1. The output of the comparatorcircuit COMP1 is connected to an input on a microelectronic processorMP, such as the 68HC05 available from Motorola. The microelectronicprocessor MP also has outputs connected to control the switching of theswitches S2-1 through S2-6, S3-1 through S3-6 and switches S1, S2 and S4mentioned previously.

As a preparatory step, switches S4 and S5 are closed, along with theappropriate switch S2-1 through S2-6 to discharge a selected positioncapacitor CA2 through CA6 and to discharge holding capacitor C3. Then,in a first detection step, with switches S4 and S5 open, the positioncapacitor CA1-CA6 is charged by closing switch S1 and the appropriateswitch S2-1 through S2-6. In a second detection step, with switches S1and S4 open, switch S5 is closed, together with the appropriate switchS2-1 through S2-6, to transfer the accumulated charge to the holdingcapacitor C3. The first and second detection steps are then repeated toincrementally increase the charge on the holding capacitor C3 until theoutput of the comparator COMP1 goes to a logic high state. Themicroelectronic processor MP counts and stores the number of transfercycles needed to switch the comparator COMP1 in this manner. Themicroelectronic processor MP then determines the capacitance of thevariable capacitance provided by the selected number wheel 13-18. Thepreparatory and detection steps are then repeated to determine thecapacitance of the reference capacitor CB1-CB5 provided by the selectednumber wheel 13-18. The method is repeated for each of the number wheels13-18. The microelectronic processor MP determines the differencebetween the variable capacitance and reference capacitance for eachnumber wheel 13-18 to determine the positions of the respective numberwheels 13-18 and the accumulated decimal count. This count may becommunicated to a human observer through one of the many digital displaydevices known in the art.

This has been a description of examples of how the invention can becarried out. Those of ordinary skill in the art will recognize thatvarious details may be modified in arriving at other detailedembodiments, and these embodiments will come within the scope of theinvention.

For example, although shafts 32a-e are shown and described forsupporting the number wheels for rotations, various other meansincluding hub assemblies are also contemplated by the invention, so asthe number wheels are supported for rotation around an axis of rotation.

Therefore, to apprise the public of the scope of the invention and theembodiments covered by the invention, the following claims are made.

We claim:
 1. A capacitive device for providing an electrical signal to adetector circuit to indicate one of a plurality of positions of amovable element to represent a count, whereinat least one movableelement comprises a rotatable element having a circumference with aplurality of positions representing successive increments in a countthat is greater than a binary count, and the device further comprising:a substrate opposite one surface of the rotatable element, the substratecarrying a stationary electrode that is spaced from the rotatableelement to form a gap for a variable capacitor; and means supporting therotatable element for rotation of the rotatable element around an axisof rotation; and further comprising dielectric material extending aroundthe circumference of the rotatable element, said dielectric materialhaving variable thickness to produce variable spacing across the gapfrom the stationary electrode to form a plurality of capacitance valuesat the plurality of positions around the circumference of the rotatableelement, wherein said plurality of capacitance values correspond to acount greater than a binary count.
 2. The device of claim 1, wherein asealing coating is provided on the electrode and the dielectric materialfor protection against moisture.
 3. The device of claim 1, wherein therotatable element is a number wheel with indicia around thecircumference of the number wheel corresponding to the plurality ofpositions.
 4. The device of claim 1, wherein the capacitance is variedby varying the spacing of the dielectric material from the stationaryelectrode on the substrate in a direction substantially parallel to theaxis of rotation of the rotatable element.
 5. The device of claim 4,wherein a sealing coating is provided on the electrode and thedielectric material for protection against moisture.
 6. The device ofclaim 4, wherein the rotatable element is a number wheel.
 7. The deviceof claim 1, wherein a sealing coating is provided on the electrode andthe dielectric material for protection against moisture.
 8. The deviceof claim 1, wherein the rotatable element is a number wheel.
 9. Thedevice of claim 1, wherein the thickness of the dielectric material isvaried in a direction along a radius from the axis of rotation of therotatable element.
 10. The device of claim 9, wherein the rotatableelement is a number wheel.
 11. The device of claim 1, wherein thethickness of the dielectric material is varied in a direction parallelto the axis of rotation of the rotatable element.
 12. The device ofclaim 11, wherein a sealing coating is provided on the electrode and thedielectric material for protection against moisture.
 13. The device ofclaim 11, wherein the rotatable element is a number wheel.
 14. Thedevice of claim 1, wherein the rotatable element carries a seconddielectric material around the circumference of said rotatable elementand disposed adjacent said first-mentioned dielectric material andvarying inversely in thickness to said first-mentioned dielectricmaterial.
 15. The device of claim 14, wherein thicknesses of the firstand second dielectric materials are varied in a direction along a radiusfrom the axis of rotation of the rotatable element.
 16. The device ofclaim 14, wherein thicknesses of the first and second dielectricmaterials are varied in a direction parallel to the axis of rotation ofthe rotatable element.
 17. The device of claim 16, wherein a sealingcoating is provided on the electrode and the dielectric element forprotection against moisture.
 18. The device of claim 16, wherein therotatable element is a number wheel.
 19. The device of claim 1, whereinthe rotatable element carries a plurality of tracks around itscircumference each having a plurality of dielectric materials to varythe capacitance of the variable capacitor as the rotatable element isrotated relative to the electrode on the substrate.